Vibrational Spectra of Salts of the Type AI3[Mo2X9], with X = Cl, Br, I

Abstract

The far-infrared and Raman spectra of a series of alkali, ammonium and alkylammonium salts of Mo2X93- (X =Cl, Br, I) have been measured. All observed infrared-active vibrations, including lattice modes, together with certain Raman-active modes, have been assigned for the alkali salts of Mo2Cl93- on the basis of the D6h unit cell symmetry which applies. The vibrational assignments for the corresponding bromide and iodide complexes follow in the same relative order as those of Mo2Cl93-. The splitting of degenerate modes for certain alkylammonium salts of Mo2Cl93- has been interpreted on the basis of C2v symmetry applicable to these particular salts. By correlating the spectral changes observed with variation of the cation, it has been possible to distinguish the bridging-halogen deformation modes from neighbouring lattice modes.